export default class ImageCompress {
  constructor(file, fileSize, maxWH = 1920) {
    this.file = file;
    this.fileSize = fileSize;
    this.maxWH = maxWH; // 最大长宽
  }

  compress() {
    // 压缩
    const fileType = this.file.type;
    const fileSize = this.file.size / 1024;
    return new Promise(resolve => {
      const reader = new FileReader();
      reader.readAsDataURL(this.file);
      reader.onload = () => {
        const canvas = document.createElement('canvas');
        const img = document.createElement('img');
        img.src = reader.result;
        img.onload = () => {
          const ctx = canvas.getContext('2d');
          const _dWH = this.dWH(img.width, img.height, this.maxWH);
          canvas.width = _dWH.width;
          canvas.height = _dWH.height;

          // 清空后, 重写画布
          ctx.clearRect(0, 0, canvas.width, canvas.height);
          ctx.drawImage(img, 0, 0, canvas.width, canvas.height);

          const newImgData = canvas.toDataURL(fileType, 0.90);

          // 压缩宽高后的图像大小
          const newImgSize = this.fileSizeKB(newImgData);

          if (newImgSize > this.fileSize) {
            console.log('图片尺寸太大!' + fileSize + ' >> ' + newImgSize);
          }

          const blob = this.dataURLtoBlob(newImgData, fileType);
          const nfile = new File([blob], this.file.name);
          resolve(nfile);
        };
      };
    });
  }

  /*
     * 长宽等比缩小
     * 图像的一边(长或宽)为最大目标值
     * */
  dWH(srcW, srcH, dMax) {
    const defaults = {
      width: srcW,
      height: srcH,
    };
    if (Math.max(srcW, srcH) > dMax) {
      if (srcW > srcH) {
        defaults.width = dMax;
        defaults.height = Math.round(srcH * (dMax / srcW));
        return defaults;
      } else {
        defaults.height = dMax;
        defaults.width = Math.round(srcW * (dMax / srcH));
        return defaults;
      }
    } else {
      return defaults;
    }
  }

  fileSizeKB(dataURL) {
    let sizeKB = 0;
    sizeKB = Math.round((dataURL.split(',')[1].length * 3 / 4) / 1024);
    return sizeKB;
  }

  /*
     * 转为Blob
     * */
  dataURLtoBlob(dataURL, fileType) {
    const byteString = atob(dataURL.split(',')[1]);
    let mimeString = dataURL.split(',')[0].split(':')[1].split(';')[0];
    const ab = new ArrayBuffer(byteString.length);
    const ia = new Uint8Array(ab);
    for (let i = 0; i < byteString.length; i++) {
      ia[i] = byteString.charCodeAt(i);
    }
    if (fileType) {
      mimeString = fileType;
    }
    return new Blob([ab], { type: mimeString, lastModifiedDate: new Date() });
  }
}
